Low voltage Global Positioning System (GPS) Low Noise Amplifiers (LNAs) operate with a supply voltage of 1.8V or less. Such amplifiers are needed for many modern portable applications.
Conventional Darlington amplifiers are noted for their wide band frequency performance, compact size, and ease of integration. Directly coupling a common-emitter amplifier with a Darlington amplifier can increase the gain and lower noise of the Darlington amplifier over a broadband. Such an implementation can be useful for multi-band wireless applications. The use of bipolar transistors to implement a Darlington uses a supply of at least 2-2.5 times the base to emitter voltage (Vbe), which would exceed the supply voltage available for low voltage portable applications. While bipolar transistors offer higher gain, lower noise, and better linearity compared to MOSFET transistors, bipolar transistors typically need more headroom voltage to operate in a radio frequency range.
It would be desirable to use a zero voltage-threshold FET device to create a low voltage Darlington that runs with a low operating voltage provides a compact 2-stage direct-coupled low noise amplifier, provides power down capability, and maintains radio frequency performance comparable to a bipolar implementation.